This invention is generally in the field of antimicrobial materials useful in the purification of fluids, purification devices including antimicrobial materials, and methods of making and using such antimicrobial materials.
There is a general need for devices and methods to eliminate microorganisms from fluids for various applications, including the provision of safe or potable drinking water and breathable purified air. Many different methods are currently used for the purification of fluids. Representative examples include distillation, ion-exchange, chemical adsorption, filtering, and retention. Oftentimes, a number of different techniques must be combined to provide complete purification of fluids. These techniques can be costly, energy inefficient, and require significant technical expertise. Unfortunately, many low cost purification techniques do not adequately treat or remove harmful biological contaminants, bacteria, and viruses.
The Environmental Protection Agency (EPA) has set forth minimum standards for acceptance of a device proposed for use as a microbiological water filter. Common coliforms, represented by the bacteria E. coli and Klebsiella terrigena, must show a minimum 6-log reduction (99.9999% of organisms removed) from an influent concentration of 1×107 per 100 mL of water. Common viruses, represented by poliovirus 1 (LSc) and rotavirus (Wa or SA-11), which show a resistance to many treatment processes, must show a minimum 4-log reduction (99.99% of organisms removed), from an influent concentration of 1×107 per 100 mL of water. Cysts, such as those represented by Giardia muris or Giardia lamblia, are widespread, disease-inducing, and resistant to most forms of chemical disinfection. A device claiming cyst-removal must show a minimum 3-log reduction (99.9% of cysts removed) from an influent concentration of 1×106 per L or 1×107 per L.
It is known to use strong oxidants, such as phenols and hypochlorites, to effectively negate the potential threat of all microorganisms in water; however, these agents must be removed from water before consumption. Known biocompatible antimicrobial agents generally destroy only select microorganisms rather than a broad spectrum of microorganisms, thereby requiring the use of multiple biocompatible antimicrobial agents to effectively negate the potential threat of all microorganisms.
One conventional biocompatible antimicrobial agent is known as chlorhexidine. Chlorhexidine is a 1,6-di(4-chlorophenyl-diguanido) hexane having the chemical formula:
The IUPAC name for chlorhexidine is N,N″Bis(4-chlorophenyl)-3,12-diimino-2,4,11,13-tetrazatetradecanediimideamide. Chlorhexidine has a high level of antibacterial activity, low mammalian toxicity, and a strong affinity for binding to skin and mucous membranes. It has been used as a topical antiseptic for application to areas such as skin, wounds, and mucous membranes. Chlorhexidine also has been used as a pharmaceutical preservative and as a disinfectant for inanimate surfaces.
Historically, chlorhexidine has been used only in its salt soluble forms. Chlorhexidine salts, however, have an extremely bitter taste that must be masked in formulations intended for oral use. In addition, chlorhexidine salts are ineffective for applications requiring insoluble materials.
Chlorhexidine's antimicrobial activity is directed mainly toward vegetative gram-positive and gram-negative bacteria. It is ineffective against bacterial spores, except at elevated temperatures. Acid-fast bacilli are merely inhibited and not inactivated by aqueous solutions of chlorhexidine. At relatively low concentrations, chlorhexidine is bacteriostatic, while at higher concentrations, chlorhexidine is rapidly bactericidal. Chlorhexidine's fungicidal activity is subject to species variation. Although chlorhexidine and its know derivatives exhibit some antimicrobial activity, they unfortunately may not be effective against a broad spectrum of microorganism types.
Other water soluble antimicrobial chemical agents are known in the art. Representative examples of such conventional materials include soaps/detergents, surfactants, acids, alkalis, heavy metals, halogens, alcohols, phenols, oxidizing agents and alkylating agents. Most of these agents chemically alter (e.g., by an oxidation reaction, etc.) the cellular structure of microbes to inactivate them. These agents may have undesirable side-effects on the affected area of contamination (skin, clothes, paint, etc.) with often deleterious side-effects (discoloration and oxidation).
Accordingly, there remains a need for an inexpensive and biocompatible antimicrobial agent that will effectively inactivate a broad spectrum of microorganisms. There is also a need for a practical purification material comprising a biocompatible antimicrobial agent for purifying fluids. Desirably, the purification material would significantly exceed the minimum EPA requirements for designation as a microbial water purifier such that it is suitable for consumer and industry point-of-use applications.